Note 49 — DESCRIPTION OF THE MINES, &c.
Reading edition
One of the vague terms sometimes given to the crust or coating of the ore, sometimes to an argillaceous substance, and sometimes to a quartz ore one. The miners have pretty generally determined, however, that caple must be black; and at Polgooth they mean a heavy kind of quartz, which is perfectly opake, and contains a large portion of argill.